1. Field of the Invention
The present invention relates to an electro-acoustic transducer which performs particularly well and is economical, including a flexible loudspeaker enclosure having a form of revolution about its axis and two loundspeakers mounted back to back in the axis of the enclosure.
The great majority of loudspeaker enclosures known up to present include two, three and sometimes four loudspeakers, skillfully connected together so as to try and cover the whole of the audible frequency spectrum. This design generally requires the insertion of a frequency dividing filter between the input of the signal and the different loudspeakers. It is known in this case that the filter alters the sound message by introducing numerous modifications therein:
very substantial reduction of the dynamic range, PA1 reduction of the overall efficiency of the enclosure, PA1 modification of the phase at the cut off frequencies which results in an increase or a decrease of the acoustic power at these frequences.
Problems are also known related to total quality disparities which are inevitable between the different loudspeakers and which adversely affect the faithfulness of the sounds reproduced.
Other sources of annoyance are related to conventional loudspeaker enclosures in which all the active loudspeakers are mounted on the front panel thus, imposing on the assembly a sound directivity forcing the listener to "locate" the optimum or privileged listening area, which is incompatible with the comfort of natural listening, all the more sensitive in the low frequency range.
Furthermore, the generally parallelepipedic shape of multichannel enclosures imposes on the rear wave of the low frequency loudspeaker, operating as a piston, a constraint which results in a prejudicial deformation of the front wave, alone transmitting the sound message. Naturally, this constraint imposed on the rear wave is more or less important depending on the acoustic absorption power of the walls or the degree of sophistication of the vents or baffles intended to attenuate the return of the wave.
Another result of the prismatic shape of the enclosures relates to the edges thereof whereon the vibrations of the loudspeakers are distorted, ruining most of the time the omnidirectional character of the same loudspeakers.
It may finally be noted the conventional observations or difficulties related to traditional cabinet making for this kind of enclosure: being generally poorly suspended, the enclosure frequently resonating and transmitting unpleasant vibrations in the environment, further added to the often unaesthetic appearance of their wooden case, to their weight and the truly unacceptable cost.
2. Description of the Prior Art
In this field of sound emitters or transducers, research work has at all times passionately interested amateurs and professionals; it is therefore not surprising that numerous solutions have been proposed to try and reduce the above mentioned drawbacks.
To reduce the space required by the loudspeaker enclosure, while keeping all the required "high fidelity" qualities, it has been proposed, as indicated in the patent FR 1 330 932, to replace the single membrane of a loudspeaker by two or more membranes moving in phase in the same direction and juxtaposed; thus the rear wave is decoupled from the front wave. In patent FR 1 510 260, interesting attempts can be found for limiting the "confident of the sound" and especially for solving the unacceptable directional character of a conventional installation seriously affecting the pattern of the acoustic radiations.
Other proposals have been set forth particularly in patent FR 2 338 616 for overcoming the distortions and resonances creating disturbances in listening; it has been more particularly proposed to replace the front loudspeakers by at least two similar loudspeakers, disposed in line behind each other, in a common support, which may be cylindrical or not, whose front end is closed by one of the loudspeakers and whose rear end is closed by the other loudspeaker mounted in acoustic phase, that is to say electrically in series or in parallel depending on the arrangement of the membrane of the rear loudspeaker.
It is now known that this type of solution remains very partial; in fact, all the drawbacks of directionality or resonance frequencies remain and are even amplified by the electric coupling of the front and rear loudspeakers, whereas the improvements obtained further increase the price of the installation.